The acknowledged drugs of choice for the pharmacological treatment of insomnia are the benzodiazepine hypnotics, but the dependence liability of these drugs remains a critical issue. Among the potential risk factors for benzodiazepine hypnotic dependence identified (no data were offered) by a recent American Psychiatric Association (APA) task force were rebound insomnia and chronic insomnia. The results of the first three years of this project unequivocally indicate that rebound insomnia is not a risk factor. On the other hand, chronic insomnia may be a risk factor. Insomnia patients were found to self-administer "hypnotics" (both placebo and active drug) at high and sustained rates beyond that seen in previous daytime studies in non-insomnia populations. Further understanding "hypnotic" (a pill taken at bedtime) self-administration in chronic insomnia patients will help clarify the dependence liability of benzodiazepine hypnotics and facilitate management of insomnia. Previous studies (all daytime in non-insomnia populations? may have no relevance to benzodiazepine hypnotic dependence. The aim of this continuation proposal is to assess the conditions for and reinforcing function of "hypnotic" self-administration in chronic insomnia patients. Controlled laboratory studies of the reinforcing and subjective effects of hypnotics with concurrent objective measurement of sleep and wakefulness will be conducted. Conditions being considered are the specific model used to study the self-administration, the specificity of time of day (bedtime vs daytime) for its occurrence, and treatment regimens (prn vs enforced nightly use) which may increase the likelihood of self-administration. To assess potentially important reinforcing properties, hypnotics, with different "euphoric-dysphoric" effects and with different sedation cues, will be compared.